1. Field of the Invention
The present invention relates to a gas-circulating processing apparatus for circulating and recycling a processing gas, and to a gas circulating and processing method.
2. Description of the Related Art
Cleaning gases such as CF4, C2F6, NF3, etc. to be employed for cleaning a chamber such as a CVD device are known as a global warming gas, so that the employment and discharge of these gas are required to be reduced as minimum as possible. In this case, a method of circulating the gas is effective in minimizing the quantity of employment and discharging of gas. As for the system for circulating and recycling the gas, there is proposed a method as set forth for example in Jpn. Pat. Appln. KOKAI Publication No. 9-251981 wherein a processing gas is circulated so as to recycle it for use in a film-forming treatment or in an etching treatment.
In the gas-circulating system as mentioned above, a processing gas (a recycling gas) from a circulating route is designed to be combined with another processing gas from an ordinary gas supply route (the gas to be supplied from the ordinary gas source), and the resultant processing gas thus combined is introduced through a confluent gas route into a chamber. In this case, in order to supply a processing gas effectively from the circulating route as well as from the ordinary gas supply route, it is important to minimize the pressure of confluent gas flow so as to increase as much as possible a pressure difference between the back pressure of a gas circulating exhaust unit (to be interposed between the chamber and the ordinary main exhaust unit) and the pressure of confluent gas flow.
In the prior art however, the aforementioned viewpoints have not been sufficiently taken into consideration with regard to the conductance of the piping (or piping) of each of the routes, so that it has been difficult to lower the pressure of confluent gas flow. When the pressure of confluent gas flow is high, the back pressure of the gas circulating exhaust unit is required to be increased, thereby making it difficult to miniaturize the gas circulating exhaust unit. When the gas circulating exhaust unit is large in size, the location for installing the gas circulating exhaust unit would be restricted, and the circulating route for the gas circulating exhaust unit would become longer. As a result, the time for circulating the gas would become longer, thus deteriorating the gas-circulating efficiency.
As described above, although a gas circulating system for circulating and recycling a processing gas has already been proposed in the past, the gas circulating system is constructed without sufficiently taking the aspects of the diameter of piping into consideration. As a result, it has been difficult to efficiently feed a processing gas to a chamber, etc.
Furthermore, when the aforementioned gas-circulating method is adopted, the processing gas that has been activated in a chamber (active species) is also permitted to enter into the gas circulating exhaust unit (for example, a turbo-molecular pump). Because of this, the gas in the exhaust unit is required to be purged by diluting the interior of the exhaust unit with a non-corrosive gas so as to prevent the interior of the exhaust unit from being corroded by the active species. Therefore, a large quantity of an inert gas such as N2 is required to be introduced into the exhaust unit in addition to the aforementioned processing gas to be employed for cleaning the chamber. However, when the cleaning is performed by circulating a gas at a high circulation rate, the partial pressure of the cleaning processing gas is caused to lower with time, thus deteriorating the cleaning efficiency.
Jpn. Pat. Appln. KOKAI Publication No. 10-122178 describes a method wherein an inert gas is directly introduced as a purging gas into the gas circulating exhaust unit so as to prevent the interior of the exhaust unit from being corroded. However, even with this method, a large quantity of the inert gas that has been introduced into the gas circulating exhaust unit is permitted to enter into the circulating routes together with the processing gas. As a result, the processing gas to be introduced into the chamber is diluted and the partial pressure of the processing gas is lowered, thus also making it difficult to avoid the problem that the cleaning efficiency is caused to deteriorate.
As mentioned above, although a method of introducing, as a purging gas, an inert gas into the gas circulating exhaust unit has been proposed for the purpose of preventing the interior of the gas circulating exhaust unit from being corroded, the processing gas to be recycled into the chamber through circulating routes is caused to be diluted by the inert gas, thus raising the problem that the cleaning efficiency is caused to deteriorate.
On the other hand, when the aforementioned gas-circulating method is adopted, a by-product such as SiO2 for instance is also permitted to circulate, thus generating the particles thereof. Due to the generating of particles of by-product, the circulating piping and the interior of chamber are soiled, raising a problem.
It may be possible to minimize the number of particles thus adhered by etching the by-products adhered to the inner surface of the circulating piping by prolonging the cleaning time. However, in that case, the quantity of processing gas such as C2F6 would be increased, thus resulting on the contrary in the obstruction of the merit of the gas circulating method, i.e. the effects thereof to minimize the quantity of employment and discharging of gas.
There is also proposed a method wherein a filter is inserted in a circulation line for the purpose of suppressing the circulation of the by-products (for example, Jpn. Pat. Appln. KOKAI Publication No. 9-251981). However, since the conductance of the circulation line is deteriorated by the provision of the filter, the load of the gas circulating apparatus would be increased, thereby raising the problem that it becomes difficult to lower the power consumption of the gas circulating apparatus and to miniaturize the apparatus. Additionally, if the filter is clogged, the conductance of the circulation line is caused to fluctuate, thereby fluctuating the processing characteristic of the circulating apparatus. There is also a problem that the maintenance of the filter such as the exchange of filter is additionally required.
As explained above, although a gas circulating system for circulating and recycling a processing gas has already been proposed in the past, due to the particles of the by-product that will be generated in the process of forming a film or in the cleaning process, there is still a problem that the circulating piping, etc. are likely to be soiled by the particles.